The microscope slide technique for manually performing blood grouping tests is not sensitive to subtle reactions and requires strict attention to protocol to avoid the possibility of sample misidentification. As an alternative to the microscope slide technique the test tube centrifuge technique has been utilized. Additionally, the test tube centrifuge technique has been used to augment or to confirm the microscope slide technique procedures. The test tube centrifuge technique has the characteristic of being more sensitive to subtle reactions than the microscope slide technique. However, the test tube centrifuge technique is more labor intensive, is subject to interpretation by the laboratory technician and has the inherent problem of assuring accurate sample identification.
The "microwell" test method has been developed to acquire the maximum utilization of the materials involved in blood grouping and to standardize the interpretation and the evaluation of biological specimens to provide more consistent results. The "microwell" test method uses a plate containing numerous small centrifuge tubes or wells.
Automated reading techniques for blood grouping have typically been limited to the measurement of turbidity. Turbidity results from the breakup of centrifuged red blood cells. A method of initiating the dissociation of red blood cells is to mix the cells with a reagent and to subject the mixture to vibration. The dissociation of the red cells is indicative of a negative reaction between red blood cells and the added reagent. If a positive reaction occurs after being subjected to vibration, the red cells remain tightly associated. The cohesive attraction of the red cells when subjected to the reagent is an indication of a positive reaction. Typically, a positive reaction between the red blood cells and the reagent yields a compact mass of red blood cells and a clear supernatant.
Turbidity may be measured based upon the opacity of the specimen. A light or energy beam is transmitted through the specimen. A detector determines the reduction in the intensity of the light or energy beam caused by the scattering or the absorption of the beam by the specimen. The turbidity of the specimen is measured as a function of the reduction in transmitted light or energy. Specifically, the reduction of the intensity of the transmitted beam is caused by the loss of light or energy due to the scattering and the absorption of the incident beam by the suspended red cells. The number of available suspended red cells is directly proportional to the amount of dissociation of red cells caused by negative reactions.
Despite important advances in the prior art, there is still a need for an automated blood grouping system and a method which reduces the subjective interpretation of reactions by laboratory personnel, which is easily used, which requires little technical expertise and few personnel, and which is comparatively inexpensive.